The present invention relates to a technique of monitoring a load state, and in particular, to a technique of detecting a symptom of transition of an information processing apparatus to a high load state.
There are known techniques of measuring performance information of an information processing apparatus to monitor a load state of the information processing apparatus and to control the load of the information processing apparatus based on the monitoring result.
For example, Abhishek Chandara, Wibo Gong and Prashant Shnoy, “Dynamic Resource Allocation for Shared Data Centers Using Online Measurements”, [online], Department of Computer Science, University of Massachusetts Amherst, [retrieved on Jan. 30, 2004], (hereinafter referred to as Non-patent Document 1) discloses a load management system in which a load is monitored by measuring an average queue length as performance information for each application, and computing resources are reallocated to applications based on increase or decrease of their loads. Operation of this load management system is outlined as follows.                (A-1) A queue length is measured for each application running on an information processing apparatus, and an average value per unit time is calculated.        (A-2) Based on the average value of queue length, which has been calculated in (A-1) for each application, a response time, extending from input of a request into the application to output of a response to that request, is estimated.        (A-3) The response time estimated in (A-2) for each application is substituted into a prescribed evaluation function, to recalculate the computing resource quantity allocated to each application.        (A-4) A computing resource of the new quantity obtained in (A-3) is allocated to each application.        
In detail, a computing resource means a CPU operating time, a usable memory capacity, and the like allocated to an application.
Further, Sally Floyd and Van Jacobson, “Random Early Detection Gateways for Congestion Avoidance”, [online], Lawrence Berkeley Laboratory, University of California, [retrieved on Nov. 30, 2004], (hereinafter referred to as Non-patent Document 2) discloses a gateway device that uses a packet control system called RED (Random Early Detection). RED measures an average value per unit time of the queue length of a buffer in the gateway device so as to monitor the load state of the gateway device, and rejects packets before the gateway device gets into a high load state. Frequently, a high load state of a gateway device occurs when a specific sender sends a large amount of packets in a short period of time. Thus, if rejection of packets starts after a gateway device gets into a high load state, packets from a specific sender are rejected intensively. RED can prevent concentration of rejected packets on a specific sender, by starting rejection of packets before a gateway device gets into a high load state.
Further, Japanese Non-examined Patent Laid-open No. 2002-252629 (hereinafter referred to as Patent Document 1) discloses a packet processing device that determines a VoQ (Virtual Output Queue) to which a right of sending packets to a cross bus switch is given, based on packet sending intervals and queue lengths of VoQs. According to this packet processing device, buffer overflow under a load imbalance can be suppressed by suppressing a delay time of a high load queue, and on the other hand, a low load queue can send packets without being affected by a high load queue.
Further, Japanese Non-examined Patent Laid-open No. 2004-56328 (hereinafter referred to as Patent Document 2) discloses a router that considers a queue length in performing controls when it notifies an available band to a user, so that it can notify occurrence of congestion in a short time. When the router receives control packets sent by a user to grasp a current state of a network, the router measures a queue length of a buffer of each priority class i. In the case where the queue length of the buffer of the priority class i is less than or equal to a threshold, a previously-calculated available band for the priority class i is notified as an available band for the priority class i to the user. On the other hand, in the case where the measured queue length of the buffer of the priority class i is larger than the threshold, 0 is notified as the available band for the priority class i to the user.
In all the above-described techniques, a queue length is measured as performance information of an information processing apparatus, and an average value (per a prescribed time) of measurement results is compared with a pre-set threshold (even in the case where a measurement result is used as it is, the measurement result can be taken as an average value per a measurement time interval), and load control processing is started when the average value exceeds the threshold. As in the case of the technique described in Non-patent Document 2, it is preferable for efficient load control that load control processing is started before an information processing apparatus gets into a high load state.
However, performance information such as a queue length or a response time shows a property (referred to as a burst) that it becomes rapidly worse when a load state of an information processing apparatus exceeds some value. In other words, a range of queue lengths corresponding to a load state (referred to as a symptom state) positioned between a high load state and a low load state is narrow. Accordingly, for the conventional techniques that compare an average value of measured values of performance information such as a queue length or a response time with a threshold, it is difficult to detect the symptom state with high precision, owing to a burst of the performance information. As a result, sometimes load control is started after a high load state occurs, or still in a low load state.
The present invention has been made taking the above situation into consideration. An object of the invention is to detect a symptom state in which a low load state shifts to a high load state.